Description: MedFlux sampling was carried out at the French JGOFS DYFAMED (DYnamique des Flux Atmospheriques en MEDiterranee) site in the Ligurian Sea (northwestern Mediterranean), 52km off Nice (431200N, 71400E) in 2300m water depth. In 2003, a mooring with sediment trap arrays was deployed 6 March (day of year, DOY 65) and recovered 6 May (DOY 126); this trap deployment will be referred to as Period 1 (P1). The array was redeployed a week later on 14 May (DOY 134) and recovered again on 30 June (DOY 181); this trap deployment will be referred to as Period 2 (P2). Indented-rotating sphere (IRS) valve traps were fitted with TS carousels to determine temporal variability of particulate matter flux. TS traps were fitted with ''dimpled'' spheres. Vertical flux at 200m depth is considered to be equivalent to new or export production, and traps sampled at 238 and 117m during P1 and P2, respectively. We also collected TS material at 711m during P1 and at 1918m during P2. Upon recovery, samples were split using a McLaneTM WSD splitter to allow multiple chemical analyses. Here we report 2003 data on TS particulate mass, and the contributions of organic carbon (OC), opal, lithogenic material and calcium carbonate to mass. In 2005, traps were deployed as described above for 55 d during a single period from 4 March (DOY 63) to 1 May (DOY 121). TS traps were fitted with ''dimpled'' spheres. TS particulate matter was collected from 313 to 924 m.

Description: Effects of CO2 concentration on elemental composition of the coccolithophore Emiliania huxleyi were studied in phosphorus-limited, continuous cultures that were acclimated to experimental conditions for 30 d prior to the first sampling. We determined phytoplankton and bacterial cell numbers, nutrients, particulate components like organic carbon (POC), inorganic carbon (PIC), nitrogen (PN), organic phosphorus (POP), transparent exopolymer particles (TEP), as well as dissolved organic carbon (DOC) and nitrogen (DON), in addition to carbonate system parameters at CO2 levels of 180, 380 and 750 µatm. No significant difference between treatments was observed for any of the measured variables during repeated sampling over a 14 d period. We considered several factors that might lead to these results, i.e. light, nutrients, carbon overconsumption and transient versus steady-state growth. We suggest that the absence of a clear CO2 effect during this study does not necessarily imply the absence of an effect in nature. Instead, the sensitivity of the cell towards environmental stressors such as CO2 may vary depending on whether growth conditions are transient or sufficiently stable to allow for optimal allocation of energy and resources. We tested this idea on previously published data sets where PIC and POC divided by the corresponding cell abundance of E. huxleyi at various pCO2 levels and growth rates were available.

Description: Coomassie stainable particles (CSP) are protein-containing transparent particles that can be stained with Coomassie brilliant blue (CBB) and are found abundantly in aquatic systems; however, their distribution and role remain poorly known, in part due to the lack of an efficient method to study them. We developed a new, simple, and low cost semi-quantitative spectrophotometric method for determination of CSP in aquatic systems. The method is analogous to that used to quantify polysaccharide-rich gel particles called transparent exopolymeric particles (TEP). CSP concentration is determined relative to bovine serum albumin (BSA) standard aggregates (in a manner similar to how TEP is quantified relative to xanthan gum). The method is based on the linear relationship between CSP concentration and the absorbance of the eluted dye from a CBB-protein complex, which has an absorbance maximum (λmax) at 615 nm. The limit of detection and the precision (%RSD) for the proposed method are 6 μg BSA equivalent and 11%, respectively. The new spectrophotometric method was validated with the existing microscopic method. This new method to quantify CSP is simple, enables rapid measurements, and allows a more efficient comparison with TEP concentrations than the present microscopic method. The spectrophotometric analyses will further the investigation of the abundance, distribution, and role of CSP in the biogeochemistry of the ocean.

Description: We measured the vertical distribution of TEP and CSP at a site on the Bermuda Rise by staining parallel samples with Alcian Blue and Coomassie Brilliant Blue, during five research cruises in 2012-2013. We used a new spectrophotometric method, analogous to that for TEP, to measure CSP concentration relative to bovine serum albumin (BSA) standard aggregates. The method is based on the linear relationship between CSP concentration and the absorbance of the eluted dye from a CBB-protein complex. TEP concentrations ranged from 23-53 µg XG eqL-1, and decreased with depth. CSP concentration ranged from 2-24 µg BSA eqL-1, and values decreased with depth, but the CSP max was slightly below that of TEP. The CSP and TEP profile shapes and loss rates were different. These differences support the idea that the two particle types have different origins. Either CSP is more labile than TEP, or TEP and CSP are produced at the same depth, but TEP ascends to the surface due to the combination of its buoyancy, and the high TEP to solid ratio found in low productivity regions.

Description: Melanoidins, condensation products of sugars and amino acids, are thought to represent a key link in the transformation of polysaccharides and proteins to humic material in the marine environment. We investigated adsorption behaviour of melanoidins prepared in equimolar solutions of glucose and amino acids of choice (glutamic acid, valine and lysine) and pseudomelanoidins which were prepared from glucose only. Melanoidins were prepared using different condensation times (2, 4, 16 and 32 days). Synthesized melanoidins were separated into different molecular mass fractions. Fractionation of melanoidins by sorption on the macroreticular resin XAD-8 separated melanoidins into hydrophobic neutral, hydrophobic acid and hydrophilic fractions. Adsorption of melanoidins and their different fractions was studied at a mercury electrode by directly measuring the change of the double layer capacitance caused by the adsorption of organic molecules on the electrode surface through phase sensitive alternating current voltammetry. The hydrophobic acid fraction of melanoidins accounted for most of the adsorption behaviour of melanoidins. Consequently, the higher molecular mass fraction of melanoidins (〉10 kDa) exhibits a stronger adsorption in comparison to the lower molecular mass fraction (〈3 kDa) of the same melanoidin. The good fit of adsorption data of melanoidins and pseudomelanoidins to the same adsorption isotherm supports the idea that melanoidins are comprised of a sugar derived “backbone” that is responsible for the adsorption behaviour of melanoidin, while the presence of nitrogen atoms is responsible for the complexation of copper ions. Adsorption characteristics and complexation ability of melanoidins and natural organic matter were similar. Our results suggest that in the process of humification, selective adsorption of condensation products on aqueous surfaces may lead to a progressive immobilization of certain fractions, i.e., it is probable that higher molecular mass components accumulate at aquatic surfaces, while lower mass components remain in solution.